A RILEM technical committee on Internal Sulfate Attack (TC 186-ISA) was established in 1996. In the ensuing years considerable research was carried out, which helped to clarify the scientific knowledge surrounding this form of degradation. A Seminar was organised in September 2002 to bring together the leading researchers in the field to debate the state of the advances made in this area. All known active researchers in the area were invited and most were able to attend. The workshop was organised with sessions designed to address the key questions related to Delayed Ettringite Formation (DEF) and Internal Sulfate Attack. In each session one or more invited presentations and several shorter presentations were made by leading researchers to summarise experimental findings and present their views. These presentations were followed by extensive discussion, at the end of which a summary was made of the main points of agreement and of areas where questions remained open. This report gives these discussion summaries as the current consensus view on this subject.